This prospective observational study aims to evaluate the time-dependent changes in Pulse Wave Transit Time (PWTT) following ultrasound-guided infraclavicular brachial plexus block. PWTT is a non-invasive hemodynamic parameter reflecting vascular tone and sympathetic nervous system activity. Patients undergoing upper extremity surgery under infraclavicular block will be monitored using standard perioperative monitoring devices. PWTT measurements will be obtained before and after block placement at predefined time intervals. Secondary outcomes will include perfusion index, skin temperature, heart rate, blood pressure, respiratory rate, and oxygen saturation. The study seeks to determine whether PWTT can serve as an objective and non-invasive marker of sympathetic blockade following infraclavicular block.

Regional anesthesia success is traditionally assessed using sensory and motor block evaluation methods that rely on patient cooperation and subjective responses to external stimuli. However, these methods may be difficult to apply in sedated, uncooperative, or communication-impaired patients. Therefore, objective and non-invasive indicators of sympathetic blockade have gained increasing interest in regional anesthesia practice.

Pulse Wave Transit Time (PWTT) is defined as the time interval between the R-wave on the electrocardiogram and the arrival of the corresponding pulse wave detected by a peripheral pulse oximeter. PWTT reflects vascular tone, arterial compliance, and hemodynamic status. Sympathetic blockade induced by peripheral nerve blocks results in vasodilation and reduced vascular resistance, potentially leading to measurable changes in PWTT. Previous studies have demonstrated the utility of objective parameters such as perfusion index, skin temperature, blood flow measurements, and PWTT in assessing block success. However, data regarding the temporal changes of PWTT following infraclavicular brachial plexus block remain limited.

The primary objective of this prospective observational study is to investigate the time-dependent changes in PWTT after ultrasound-guided infraclavicular brachial plexus block. The study will be conducted in patients undergoing upper extremity surgery under infraclavicular block at Sakarya Training and Research Hospital.

Patients scheduled to receive infraclavicular block as part of their routine clinical care will be enrolled after providing informed consent. The block procedure is not performed for research purposes and represents standard clinical practice. Following block administration, PWTT values will be recorded from the blocked extremity using standard monitoring equipment. Measurements will be obtained before block placement and at 0, 5, 10, 15, and 20 minutes after block completion. Baseline PWTT measurements will also be obtained from the contralateral upper extremity.

Secondary outcome measures will include perfusion index, skin temperature of both upper extremities, heart rate, non-invasive blood pressure, respiratory rate, and oxygen saturation. Demographic and clinical data will also be recorded.

All measurements will be collected according to a predefined protocol using standardized monitoring equipment. Since PWTT is an objective device-derived parameter, observer dependency is expected to be minimal. Data collection personnel will be separated from the clinician performing the block whenever feasible to reduce measurement bias. All collected data will be anonymized prior to statistical analysis.

This study is designed as a single-center, prospective observational investigation without randomization or intervention beyond routine clinical care. The findings may contribute to the development of PWTT as a practical, objective, and non-invasive marker of sympathetic blockade following infraclavicular brachial plexus block.

Inclusion Criteria:

• Patients undergoing elective upper extremity hand surgery
• 18 - 65 years
• ASA I
• No coagulopathy, thrombocytopenia, coagulation disorders
• Patients who provide informed consent to participate in the study

Exclusion Criteria:

• History of drug allergy relevant to study procedures or local anesthetics
• Body mass index (BMI) ≥ 30 kg/m²
• Body weight < 40 kg
• Age < 18 years or > 65 years
• History of significant cardiac disease (e.g., arrhythmia, conduction abnormalities)
• Coagulopathy (INR > 1.5 or platelet count < 100,000/mm³)
• Pregnancy or lactation
• Infection at the site of peripheral nerve block
• ASA II-IV
• Failed block or motor block duration exceeding 30 minutes
• Patients reporting pain (NRS ≥ 3), due to potential influence on sympathetic activity
• Chronic opioid use

The study population will consist of adult patients aged 18-65 years with ASA physical status I who are scheduled to undergo elective upper extremity hand surgery under ultrasound-guided infraclavicular brachial plexus block. All participants will receive standard-of-care anesthesia management. Patients with contraindications to peripheral nerve block, significant systemic disease, obesity (BMI ≥30 kg/m²), coagulation disorders, opioid use, or conditions affecting sympathetic activity will be excluded. Only patients who provide informed consent will be enrolled.